Allow multiple "git_path()" uses

Allow multiple "git_path()" uses

This allows you to maintain a few filesystem pathnames concurrently, by
simply replacing the single static "pathname" buffer with a LRU of four
buffers.

We did exactly the same thing with sha1_to_hex(), for pretty much exactly
the same reason. Sometimes you want to use two pathnames, and while it's
easy enough to xstrdup() them, why not just do the LU buffer thing.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>